1. Field of the Invention
The present invention relates to a hub unit to which a wheel and a disc rotor of a disc brake apparatus are mounted and other vehicle-use bearing apparatuses. More particularly the present invention relates to a vehicle-use bearing apparatus provided with a double row rolling bearing with vertex of contact angles outside of bearing on an outer periphery of a hub wheel.
2. Description of the Related Art
In a conventional vehicle-use bearing apparatus a cylindrical recessed portion is formed at an axial end of a hub wheel. The portion is bent and deformed radially outward and caulked onto an outer end face of an inner ring of a rolling bearing by using a rolling caulking jig to thereby prevent the rolling bearing from coming off the hub wheel and to apply pre-load to the rolling bearing.
The hub wheel is formed by using steel material such as JIS (Japanese Industrial Standards) S40C to S58C and SUJ2, for example. Such material includes sulfur for convenience in turning and in order to obtain stability of quality. For example, a percentage of sulfur content in steel material is specified to be 0.035% by weight or less when the steel material of JIS S40C to S58C is used as the steel material for the hub wheel and a percentage of sulfur content in steel material is specified to be 0.025% or less when the steel material of SUJ2 is used respectively in terms of convenience in turning and stability of quality for the steel material.
The present inventors found that a minute crack occurred in the caulked portion when rolling caulking was carried out and pursued study of it. As a result, because a percentage of sulfur content in the steel material to be used was set at an upper limit value or a value approaching the upper limit value in order to further improve a turning property and stability of quality, manganese sulfide was liable to be generated in the steel material by chemical combination of sulfur with manganese included in the steel material. The manganese sulfide which is a nonmetallic inclusion generated in the steel material became a starting point of a crack in the rolling caulking. Then, the inventor further pursued study and found a percentage of sulfur content with which the crack could be suppressed.
Therefore, it is a main object of the present invention to provide a vehicle-use bearing apparatus in which occurrence of a minute crack in a caulked portion can be suppressed in processing of the caulked portion by properly adjusting a specified percentage of sulfur content in steel material.
Other objects, features, and advantages of the invention will become apparent from the following descriptions.
In brief, a vehicle-use bearing apparatus according to the present invention includes a hub wheel formed of steel material to which a wheel is mounted and a rolling bearing mounted to an outer periphery of the hub wheel. An end portion of the hub wheel is expanded radially outward toward an inner ring provided to the rolling bearing to be formed into a caulked portion.
A percentage of sulfur content is adjusted to be 0.020% by weight or less with which occurrence of a crack starting from manganese sulfide in forming the caulked portion can be suppressed in steel material of which the caulked portion is formed.
In case of the present invention, the percentage of sulfur content is adjusted to be 0.020% by weight or less with respect to the specification. Thus generation of manganese sulfide or a nonmetallic inclusion can be suppressed and occurrence of the minute crack starting from manganese sulfide in the caulked portion in processing of the caulked portion can be suppressed. As a result, few vehicle-use bearing apparatuses have to be discarded due to the minute crack generated in the caulked portion and a supply performance of the product can be improved.
In the present invention, preferably, a steel type of the steel material of which the caulked portion is formed is one selected from among JIS S40C to S58C including 0.37% by weight to 0.61% by weight carbon, SAE 1040 to 1095 including 0.37% by weight to 1.03% by weight carbon, SUJ1 to SUJ5 including 0.95% by weight to 1.10% by weight carbon, and SAE 52100 including 0.98% by weight to 1.10% by weight carbon. A percentage of sulfur content in the selected steel material is preferably adjusted to be 0.020% by weight or less.
With such adjustment, because occurrence of the minute crack in the caulked portion can be suppressed while maintaining a turning property of material in forming a caulking cylindrical recessed portion by inclusion of sulfur, few products have to be discarded to thereby improve the supply performance of the product.